1. Field of the Invention
The invention concerns a convection-radiation system for heat treatment of a continuous strip.
2. Description of the Prior Art
Continuous strips or deposits on continuous strips require heat treatment. The heat treatment must often be carried out without contact in order to preserve the quality of the surface state of the strip or the deposit on it. This applies, for example, to paper strips that have undergone a wet treatment such as the treatment to produce art paper.
There are currently two different techniques for heat treating continuous strips without contact:
either continuous strip heating using infrared radiant elements, PA1 or heating by means of hot air blower elements. PA1 the blower devices are not perfectly protected from the radiation from the infrared emitters, and PA1 the blown air can disturb correct operation of the infrared radiation emitter. PA1 the infrared radiant elements deliver a high power density, and PA1 the volumes of air blown are at least 30% smaller than those circulating in an installation using only hot air. PA1 aspirate to the exterior air charged with water vapor from the strip when it is to be dried, air blown by the blower elements and combustion gases from the infrared radiant elements when the latter are of the gas-fired type, and PA1 effectively protect the blower elements from the radiation from the infrared radiant elements, the blower systems requiring dimensional stability to operate correctly.
Infrared radiant elements have a very high power density (power per unit surface area) which means that heat treatment can be carried out using a relatively compact installation.
However, the use of such radiant elements requires the use of means for supporting the continuous strip, which support means must not under any circumstances enter into contact with the paper strip.
Hot air heating systems have the drawback of a much lower power density than systems using infrared radiant elements and so they are much larger overall than a system using infrared radiant elements to carry out the same heat treatment.
On the other hand, this type of installation does not require any auxiliary means to support the strip; this function being assured by the air, which can also produce corrugations in the strip to increase its stiffness in the direction perpendicular to its motion.
One example of an installation of the above type is described in international application WO 95/14199.
Attempts have been made to combine the two techniques described hereinabove in order to associate their respective advantages.
One such attempt is described in European patent 0 291 832 or U.S. Pat. No. 5,261,166. However, the solution described in the above patent is not perfect for at least the following reasons:
The aim of the present invention is to remedy the drawbacks of the above techniques by creating an installation for drying a continuous strip that is of small overall size, delivers a high heating power density and provides a solution to the problem of supporting the continuous strip.